Piping systems in refinery and other oil and gas plants make use of welded pipe sections of various sizes. Such pipe sections are subject to varying temperature and pressure conditions which can lead to failures, particularly at the welded pipe joints. One such failure mechanism is referred to as carbonate stress corrosion cracking, which is a common problem within fluid catalytic cracking units, especially in the main fractionator overhead condensing and reflux systems, the downstream wet gas compression systems, and the sour water systems emanating from the foregoing. Carbonate stress corrosion cracking results in leakage and cracking in carbon steel and low alloy steel piping weldments if appropriate post-weld heat treatment is not adequately performed.
When a cracking indication is detected in these systems at the weld locations, a temporary repair in the form of an external clamp is normally applied. The clamp is designed to protect the pipe against full separation while the plant is still in operation.
A variety of clamps have been proposed in the past for the temporary repair of refinery piping systems. U.S. Pat. Nos. 4,049,296, 4,171,142, and 4,709,729 illustrate such clamps having divided clamp bodies which can be installed around continuous piping in bridging relationship to a joint. These types of clamp are deficient, however, inasmuch as they do not provide any self-tightening feature which causes the clamp to effect a tighter gripping relationship with the pipe sections as the latter tend to separate. U.S. Pat. Nos. 4,127,289 and 4,832,379 and Published Application 2005/0052023 disclose pipe couplings having toothed pipe-engaging segments. However, these units do not include separable clamp bodies, and thus cannot be applied to continuous piping around existing joints.
There is accordingly a real and unresolved need in the art for improved clamp assemblies which can be installed on interconnected ends of opposed pipe sections in bridging relationship to connection joints, and which afford a self-tightening feature such that the clamp assemblies exert an increased gripping force in the event that the interconnected pipes begin to separate.